Add an environment variable ICDIFF_DEFAULTS to allow setting default flags
          #191
        
          
      
  Add this suggestion to a batch that can be applied as a single commit.
  This suggestion is invalid because no changes were made to the code.
  Suggestions cannot be applied while the pull request is closed.
  Suggestions cannot be applied while viewing a subset of changes.
  Only one suggestion per line can be applied in a batch.
  Add this suggestion to a batch that can be applied as a single commit.
  Applying suggestions on deleted lines is not supported.
  You must change the existing code in this line in order to create a valid suggestion.
  Outdated suggestions cannot be applied.
  This suggestion has been applied or marked resolved.
  Suggestions cannot be applied from pending reviews.
  Suggestions cannot be applied on multi-line comments.
  Suggestions cannot be applied while the pull request is queued to merge.
  Suggestion cannot be applied right now. Please check back later.
  
    
  
    
I'm not 100% happy with this because there's no way to override boolean
options using
optparse. i.e. ifICDIFF_DEFAULTS=-Nthere is no wayto override that on the command line.
Switching to
argparsewould allow that viaBooleanOptionalActionbutthat requires python 3.9.
With
optparse, I could also addno-XXXflags for all the existingboolean flags - LMK.
I use the exact string I put in the
READMEFYI. I set that up in my VCS but I'd like to have it in effect all the time.